Hamilton Pool Preserve is a natural pool that was created when the dome of an underground river collapsed due to massive erosion thousands of years ago. The pool is located about 23 miles (37 km) west of Austin, Texas off Highway 71. Since the 1960s, Hamilton Pool has been a favorite summer swimming spot for Austin visitors and residents. Hamilton Pool Preserve consists of 232 acres (0.94 km2) of protected natural habitat featuring a jade green pool into which a 50-foot (15 m) waterfall flows. The pool is surrounded by huge slabs of limestone that rest by the water's edge; large stalactites grow from the ceiling high above. The ceiling and surrounding cliffs of the grotto are home to moss, maidenhair fern and cliff swallows. The Ashe juniper (cedar) uplands of the preserve are home to the endangered golden-cheeked warbler.

The natural pool and creek are not chemically treated, so water quality is monitored regularly and swimming is occasionally restricted; call ahead to check conditions before your visit. Hamilton Pool is part of the Balcones Cayonlands Preserve and is a protected environment. There are no lifeguards on duty, and drinking water and concessions are not available. Composting toilets and picnic tables are provided near the parking lot. Since Hamilton Pool is a nature preserve, the following rules apply: no fishing, mountain biking, camping, dogs or other pets. Cooking and fires are also not permitted.

Prior to the 19th century, the Tonkawa and Lipan Apaches lived in the area. In the mid-1860s, Morgan C. Hamilton owned the property now known as Hamilton Pool Preserve. His brother, Andrew Jackson Hamilton, evidently visited the grotto while serving as Texas governor (1865-66). In the 1880s, the Reimer family, immigrants from Germany, bought the property to raise sheep and cattle. Legend has it that their eight-year-old son discovered the collapsed grotto.

Although ranchers might have considered the grotto a safety hazard for their livestock, the Reimers soon realized its value as a recreational area and opened the property for public use. Around the turn of the 20th century, only a handful of people had the transportation to come out and enjoy the cool, serene surroundings. By the 1960s, and on into the 1980s, Hamilton Pool's popularity had soared, as visitors packed the legendary swimming hole. The land suffered from sheer numbers and few restrictions.

In addition to impact from the visiting public, cattle, sheep and goats grazed the delicate ecosystem for several decades, resulting in changes to the native vegetation. In 1980, the Texas Parks and Wildlife Department cited Hamilton Pool as the most significant natural area in rural Travis County. In 1985, Travis County purchased 232 acres (0.94 km2) from the Reimers family and implemented an aggressive land management plan to restore Hamilton Pool. Now, as Hamilton Pool Preserve, the lush fern-canopied cliffs are making a comeback, as are the rolling hills and meadows of the uplands.